1. Field of the Invention
This invention relates to polymerizable compositions of an unsaturated linear polyester. More particularly, the invention relates to polymerizable mixtures of unsaturated polyesters having improved fire retardant properties and the process of making such polyester compositions.
2. Description of the Prior Art
The production of infusible insoluble polyester resins which are flame-retardant and have a high resistance to heat is of considerable commercial importance. For instance, castings, moldings, and foamed articles on laminated structures bonded by polyester-type resins are, for many uses, desirably resistant to fire and/or are self-extinguishing. Structural members, such as pipes, wall coverings, panels, ash trays, etc. are further illustrations where flame-retardancy and/or self-extinguishing properties are desirable.
A number of flame-resistant unsaturated polyester resin compositions are known. One class of flame-resistant polyester resins contains Het acid (1,4,5,6,7,7-hexachlorobicyclo[2,2,1]-5-heptene-2,3-dicarboxylic acid) or its anhydride in the polyester composition. However, it is generally necessary to add phosphoric compounds in order to obtain the desired properties. Other flame-resistant polyester resin compositions contain fire retardant additives such as antimony trioxide or halogenated compounds such as halogenated hydrocarbons or halogenated phosphates, etc. These flame resistant polyester resins suffer from the disadvantage of producing products with a poor color stability. Still other fire resistant polyester resins have terminally located phosphonate groups built into the polyester structure as described, for example, in U.S. Pat. No. 3,150,208. Such polyester resins, however, are generally of poor stability and mediocre color.
Still other fire resistant unsaturated polyester resins contain bromine incorporated into the polyester molecule in an effective amount. For example, bromine is incorporated into an unsaturated polyester composition by direct bromination of a linear unsaturated polyester as disclosed, for example, in U.S. Pat. No. 3,536,782. However, such bromine-containing unsaturated polyesters are generally unacceptable in that high bromine concentrations are generally required in order to produce an effective level of fire retardancy.
Another class of bromine-containing unsaturated polyester resins of improved fire-retardance are those taught by U.S. Pat. No. 3,585,254 wherein the half-ester of 4-cyclohexene-1,2-dicarboxylic anhydride (tetrahydrophthalic anhydride) and a polyol is brominated and the resulting product is thereafter reacted with a dibasic acid, such as maleic anhydride to complete the esterification to form the bromine-containing unsaturated polyester resin. Such polyester resin compositions suffer from the disadvantages of involving multi-step processes in their manufacture and produce an unsaturated polyester with a very high bromine concentration; e.g., 18 wt. % and higher.
From the foregoing, it can be readily seen that many attempts to fire retard the unsaturated polyester resins have been made but have always left much to be desired.
It is therefore an object of this invention to develop a fire retardant unsaturated polyester resin which avoids the aforementioned problems. It is also an object of this invention to develop a process whereby said fire retarding and/or self-extinguishing properties are accomplished in a one-step process.
It is yet another object of this invention to develop a process for the preparation of a fire retardant unsaturated polyester resin composition which retains its color, clarity and stability and has superior fire extinguishing properties at low bromine concentrations.
Still further objects of the present invention will become apparent from the detailed description given hereinafter.